1. Field of the Invention
This invention relates to a method of manufacturing a liquid crystal display device. More specifically, the invention relates to a method of manufacturing a liquid crystal display device including a vertically aligned liquid crystal having a negative dielectric anisotropy and a polymer polymerized by light or heat for regulating a pre-tilt angle of liquid crystal molecules and a tilting direction thereof when a voltage is applied.
2. Description of Related Art
A conventional liquid crystal display device of the MVA (Multi-domain Vertical Alignment) type (hereinafter referred to as “MVA-LCD”) includes liquid crystal of the vertically aligned type having negative dielectric anisotropy, and an alignment regulating structure such as a linear protrusion or a slit formed on the substrate. In the MVA-LCD, alignment of liquid crystal is controlled by the alignment regulating structure in a plurality of directions in a pixel when a voltage is applied without rubbing treatment.
As compared to the liquid crystal display device of the TN (twisted nematic) mode, the MVA-LCD has an advantage of excellent viewing angle characteristics as well as a disadvantage of low white brightness and dark display. The principal cause of this disadvantage stems from the fact that a region on the alignment regulating structure becomes a boundary which divides the alignment of liquid crystal and optically appears to be a dark region decreasing the light transmission factor of the pixels as a whole. To improve this, the gap between the alignment regulating structures may be broadened to a sufficient degree. In this case, however, the alignment regulating structure relatively decreases, and an extended period of time is required before the alignment is stabilized, and a response time becomes long.
To realize the MVA-LCD featuring a high brightness and a high response speed, there has been proposed a method of regulating a pre-tilt angle of the liquid crystal molecules and the tilting direction when a voltage is applied by using a polymer. According to this method, a liquid crystal composition which is a mixture of liquid crystal and a monomer (polymerizable component) to be polymerized by light or heat, is sealed between two substrates. A predetermined voltage is applied between the substrates, the liquid crystal layer is irradiated with a UV ray in a state where the liquid crystal molecules are tilted and are aligned in a predetermined direction, and the monomer is polymerized to form a polymer. Due to the polymer formed near the surfaces, the direction of alignment of liquid crystal molecules and the pre-tilt angle thereof are regulated even after the voltage is no longer applied. By regulating the direction of alignment of liquid crystal molecules and the pre-tilt angle thereof by the polymer, there is obtained an MVA-LCD featuring a high brightness and a high response speed.
In recent years, further, attention has been given to a drop-injection method (One Drop Filling method) by which the substrates are attached together and, at the same time, liquid crystal is filled. According to the drop-injection method, a sealing material is, first, applied along the periphery of one substrate like a frame. Next, a predetermined amount of liquid crystal is dropped onto, for example, the other substrate. In this case, the liquid crystals are dropped onto a plurality of places on the substrate by using a dispenser. Next, the two substrates are attached together in vacuum, and the pressure is returned back to the atmospheric pressure, so that the liquid crystal is filled into between the two substrates. Use of the drop-injection method makes it possible to greatly shorten the time for injecting the liquid crystal and to simplify the steps for manufacturing the liquid crystal display device.
However, when the drop-injection method is employed to manufacture the MVA-LCD having a polymer to regulate a pre-tilt angle of liquid crystal molecules and a tilting direction thereof when a voltage is applied, it is difficult to obtain good display quality because bright dots are often seen continuing like circles along the outer peripheries of the portions where the liquid crystal composition is dropped.